1. Field of the Invention
The present invention relates to self-extinguishing compositions based on thermoplastic polymers or on polymers endowed with elastomeric properties, especially olefinic polymers and copolymers, containing particular triazinic compounds combined with phosphates and/or phosphonates of ammonium or of an amine.
2. Discussion of the Background
In the art there are known different solutions to reduce or remove the combustibility of polymers. Some of these solutions are based on the use of metal compounds, especially antimonium, bismuth or arsenic compounds, in combination with organic compounds partially halogenated and thermically unstable, such as chlorinated paraffinic waxes.
Other solutions are based on the use of substances able to produce intumescence. Formulations of intumescent type are generally consisting of the polymer and of at least three mainly additives: one essentially phosphorated, the purpose of which is to form during the combustion an impermeable, semisolid, vitreous layer, essentially consisting of polyphosphoric acid, and to activate the formation process of the intumescence, a second containing nitrogen which acts as foaming agent and a third containing carbon which acts as carbon donor to form an insulating cellular carbon layer (char) between the polymer and the flame.
Examples of intumescent formulations of this type are those reported in U.S. Pat. No. 3,810,862 (Phillips Petroleum Co.) consisting of melamine, pentaerhythritol and ammonium polyphosphate, U.S. Pat. No. 4,727,102 (Vamp s.r.l.) consisting of melamine cyanurate, an hydroxyalkylderivative of isocyanuric acid and ammonium polyphosphate, and in Published Patent Application WO 85/05626 (Plascoat U.K. Ltd.) consisting of different phosphorus and nitrogen compounds among which, in particular, a combination of melamine phosphate, pentaerhythritol and ammonium polyphosphate.
In more recent formulations, together with the use of an organic or inorganic phosphorus compound an organic compound has been used containing nitrogen, especially an aminoplastic resin obtained by condensing urea, melamine or dicyandiamide with formaldehyde.
Examples of formulations consisting of two additives are those reported in U.S. Pat. No. 4,504,610 (Montedison S.p.A.), consisting of oligomeric derivatives of 1,3,5-triazine and ammonium polyphosphate, and European Patent 14,463 (Montedison S.p.A.) consisting of organic compounds selected from benzylguanamine and reaction products between aldehydes and several nitrogenous cyclic compounds, in particular benzylguanamine-formaldehyde copolymers, and ammonium polyphosphate.
It is also possible to obtain self-extinguishing compositions using monocomponent additives, containing in the organic molecule both nitrogen and phosphorus, as described in U.S. Pat. No. 4,201,705 (Borg-Warner Corp.).
These intumescent retarding systems give the property of forming a carbon residue to the polymer containing them following a fire or application of a flame. Retarding systems of this type show many advantages: absence of corrosion phenomena in apparatus in which polymers are processed, lower emission of smokes in comparison with systems containing metal compounds and halogenated hydrocarbons and, in particular, the possibility of giving satisfactory antiflame properties to polymers using a lower quantity of total additive and therefore without an excessive decay of the mechanical properties of polymers themselves.